2004 Salem's Lot: end includes orderly finding Father Callhan smothered but with blood transfusion going to someone else. Meaning & who was that guy?

[Jack630]

Salem's Lot 2004 ending question: what was up with Father Callahan transfusion scene? who was the other guy at end of transfusion, just a random patient? did mark really smother Callahan before the transfusion? just asking if anyone knows or what you think. thanks